1. Field of the Invention
The present invention relates to silicon carbide semiconductor devices, and particularly to a silicon carbide semiconductor device having a JBS (Junction Barrier controlled Schottky diode) or MPS (Merged P-i-N/Schottky diode) structure using silicon carbide.
2. Description of the Background Art
Silicon carbide used for silicon carbide semiconductor devices has dielectric breakdown electric field that is about ten times that of silicon, and band gap that is about three times wider than that of silicon. Accordingly, power devices using silicon carbide are lower-resistant and higher-temperature operable as compared with currently available power devices as semiconductor devices using silicon. Particularly, SBDs (Schottky barrier diodes) and MOSFETs using silicon carbide are showing great promise because their losses during operation are smaller as compared with currently available silicon pn diodes and IGBTs at same withstand voltages. Especially, Schottky diodes, having simpler device structures, are under intensive development for practical use.
Problems of Schottky diodes are that the leakage current at the time of application of a reverse bias is large when higher withstand voltages are desired, and that the loss at the time of current conduction is large. For measures against these problems, JBSs (Junction Barrier controlled Schottky diodes) and MPSs (Merged P-i-N/Schottky diodes) are proposed. Both structures are characterized in that P type regions are formed under the Schottky electrode, at the ends of the electrode, and in the vicinity of the electrode.
In U.S. Pat. No. 3,630,594, for example, P type regions with different depths and different concentrations are formed under the Schottky electrode and at the ends of the electrode. In this case, it is necessary to perform ion implantation twice, in order to form the different P regions. Also, in U.S. Pat. No. 3,551,154, P type regions with the same depth and same concentration are formed under the Schottky electrode, at the ends of the electrode, and in its vicinity, but it has no alignment mark for mask arrangement. Accordingly, characteristics tend to vary due to misalignment.
For conventional silicon carbide JBS or MPS structures, it was difficult to manufacture silicon carbide semiconductor devices with suppressed variations in characteristics without increasing the number of process steps.